1. Field of the Invention
The present invention relates to a wet electrophotographic printer, and more particularly, to a wet electrophotographic printer with an improved transfer unit for transferring a toner image left on a photosensitive belt.
2. Description of the Related Art
In general, an electrophotographic printer such as a laser printer is an apparatus in which an electrostatic latent image is formed on a photosensitive medium such as a photosensitive drum or a photosensitive belt, and the electrostatic latent image is then developed by a toner having a predetermined color and transferred on a recording sheet to obtain a desired image. Laser printers are generally divided into the wet laser printer type and the dry laser printer type depending upon the kind of toner employed. The wet laser printer employs a developing solution mixed with a toner in a volatile liquid carrier. The wet laser printer employing such a developing solution is better with respect to printing performance than the dry laser printer employing a powdered toner. Moreover, since problems caused by powdered toner dust can be avoided, the wet laser printer is increasingly becoming the preferred type.
FIG. 1 is a schematic diagram showing important parts of a wet laser printer as a kind of a conventional wet electrophotographic printer.
Referring to FIG. 1, a general wet laser printer includes a photosensitive belt 110 having an endless track, a first carrier roller 121, a second carrier roller 122, and a third carrier roller 123 for rotatably moving the photosensitive belt 110 in a given path. Generally, the third carrier roller 123 is driven by a driving motor (not shown) to rotate the photosensitive belt 110. The second carrier roller 122 is a steering roller for adjusting a tensile force applied to the photosensitive belt 110 to prevent the meandering of the photosensitive belt.
Also, there is provided a main charger 135 installed on one side of the photosensitive belt 110 for uniformly charging the photosensitive belt 110. A plurality of electrostatic latent units (laser scanning units) 130 are formed in the lower portion of the photosensitive belt 110 for scanning a laser beam onto the photosensitive belt 110 according to an image signal and forming an electrostatic latent image thereon. A developer 140 is installed for developing the electrostatic latent image such that a developing solution composed of a toner having a predetermined color and a liquid carrier adheres to a portion of the belt where the electrostatic latent image is formed. In the case of a color printer, there are provided a plurality of electrostatic latent image forming units 130 for color combination and a developer containing a plurality of kinds of developing solution each having a predetermined color.
The developing solution adhering to the photosensitive belt 110 by the developer 140 is dried by a drier 150 provided along the path of the photosensitive belt 110 after the developer 140 so that the liquid carrier is eliminated, thereby forming a toner image with only the toner from the electrostatic latent image of the photosensitive belt 110.
The toner image is transferred to a recording sheet 126 by a transfer roller 124 installed in parallel with and opposing the first carrier roller 121 with the photosensitive belt 110 interposed therebetween. The recording sheet 126 is supplied between the transfer roller 124 and a pressing roller 125 installed in parallel with and opposing the transfer roller 124 at a predetermined interval. The toner image transferred on the recording sheet 126 is fixed by separate fixation means (not shown), thereby obtaining a desired image.
However, the transfer roller 124 and the pressing roller 125 are spaced apart from the first carrier roller 121. At the time of transferring the toner image to the recording sheet, since the transfer roller 124 and the pressing roller 125 simultaneously collide against the first carrier roller 121, an instantaneous shock is generated. The vibration due to the shock is transferred to the developer 140 via the photosensitive belt 110, so that the developing solution may not adhere to the electrostatic latent image formed in the photosensitive belt 110.